TRANSPORTING AND METERING PARTICULATE MATERIAL

Abstract: An improved apparatus (30) for transporting the metering particulate material (40) including a transport duct (36) having an inlet (32), an outlet (34), and at least one moving surface (31) located therebetween having a downstream facing drive surface. The apparatus further includes drive device for moving the moving surface (31) between the inlet (32) and the outlet (34) towards the outlet, and means for compacting the particulate material sufficiently to cause the formation of a bridge composed of substantially interlocking particulate material (40) spanning the width of the transport duct (36). The apparatus is used to transport and meter particulate material under ambient conditions and against pressure.

Description: TRANSPORTING AND METERING PARTICULATE MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to apparatuses and methods for transporting and metering particulate material and, in particular embodiments, to an improved particulate material handling device which can be used to both transport and meter solid material of a great range of sizes under both ambient conditions and against pressure. 2. Description of Related Art A wide variety of eguipment has been used to either transport or meter particulate material (such as, but not limited to, coal, other mined materials, dry food products, other dry goods handled in solid, particle form) . Such transport equipment includes conveyor belts, rotary valves, lock hoppers, screw-type feeders, etc. Exemplary measurement or metering devices include weigh belts, volumetric hoppers and the like. In order to provide both transport and metering of particulate material, it was typically necessary to use or combine both types of devices into a system. However, some of applicant's prior pump devices were provided with the capability of both transporting and metering particulate material. Examples of such prior designs include the rotary disk type pumps discussed in the following U.S. patents, each of which is assigned or licensed to the assignee of present invention and each of which is incorporated herein by reference: U.S. Patent No., 4,516,674 (issued May 14, 1985); U.S. Patent No. 4,988,239 (issued January 29, 1991); and U.S. Patent No. 5,051,041 (issued September 24, 1991). While some of these prior pump designs have shown some capacity to pump particulate material against a relatively low pressure head, such pumps have not been capable of pumping against a significantly larger gas or fluid pressure head. The present inventor has found that particulate solids moving through a pumping system may encounter various forces (e.g, undesirable components of drive forces, frictional forces or gravitational forces) at different locations and at different directions within the system. These forces may inhibit or even stop the normal flow of the particulate solids at certain regions or areas at or around the inlet. This may cause the particulates to eventually bridge across the inlet and stop the particulate flow through the inlet. To illustrate this, Fig. 1 shows a rotary disk type solids pump 10, which has a housing (not shown) , an inlet 12 and an outlet 14. A transport channel 16 extends between the inlet 12 and the outlet 14. The transport channel 16 is formed between substantially opposed faces of two rotary disks (one is shown at 17, the other is not shown in the figure) movable relative to the housing between the inlet 14 and the outlet 16 towards the outlet 14 and at least one arcuate wall extending between the inlet 12 and the outlet 14. The pump 10 tends to impart a tangential force or thrust 18 on the particulate solids 20 in the direction of rotation 22 of the disks 17. At the inlet 12, this tangential thrust 18 tends to force the particulate solids 20 against a stationary wall 24. As a result, the particulate solids 20 at the side of the stationary wall 24 create a mass of slow moving or stationary solids in a "dead region" 28 at or adjacent the inlet 12. This dead region 28 can reduce the rate of flow of material into the pump (and, thus, reduce the pumping rate) . The build-up and/or possible collapse of a mass of particles in the dead region can cause fluctuations in the rate of flow of material through the pump and can, thereby, adversely affect the metering accuracy of the system. In systems pumping against a gas or fluid pressure or against a pressure head formed of particles, it may be important to maintain an unobstructed pump inlet so that the pump remains full of particulate material at all times to act as a pressure barrier. Moreover, with certain particulate materials, the stagnation of the particles at the dead region 28 can cause further problems. For example, when food materials are conveyed through the pump 10, the food material held for an extended period at the dead region 28 may spoil or deteriorate and present a serious health problem. As another example, certain types of materials with a relatively high moisture content, when held for an extended period in the dead region 28, tend to become pliable and gummy, and more difficult to handle. Therefore, it would be desirable to provide an apparatus for driving or pumping the particulate solids having an inlet designed to minimize or avoid the formation of a dead region 28 in which particles are slowed or stopped. The ability of an apparatus to apply drive force to a given type of particulate material is dependent upon a number of factors relating to the design and configuration of the apparatus. The design and configuration of some prior apparatuses makes them unsuited for certain applications requiring a relatively large amount of drive force and/or an efficient transfer of the drive force to the particulate material. For example, in certain applications, it may be necessary to transport a particulate material against a resistance, for example, vertically upward against gravity, up an incline, against a pressure head and/or over a relatively large distance. Therefore, it would be desirable to provide an apparatus and method for transporting and metering a wide variety of particulate materials with an improved ability to apply drive force to the particulate materials. There are many instances in which it is desirable to transport and meter particulate materials against pressure (e.g.. wherein gas and/or fluid pressure at the output side of the transport system is greater than the gas and/or fluid pressure at the input side of the system) . It would be desirable to provide an apparatus which is capable of pumping and metering under both ambient pressure conditions and against a pressure head caused either by entry into a pressurized environment (wherein the gas and/or fluid pressure of the environment on the output side of the apparatus is greater than such at the input side) . A number of factors must be considered in the design of an efficient device for transporting or metering particulate materials. For example, the amount, size and type of particulate material to be transported must be taken into consideration. The distance over which the material is to be transported and variations in the surrounding pressure during transport must also be taken into account. It would be desirable to provide a pump device which is capable of transporting and metering a wide variety of particulate materials under both ambient and pressurized conditions. Large scale transport and/or metering of particulate material presents unique problems. A transport apparatus or system which is suitable for transporting one type of particulate material may not be suitable for transporting a different type of material. For example, Kentucky coals maintain reasonable integrity when transported through conventional devices such as screw feeders and conveyor belts. However, Western United States coals tend to be more friable and may be degraded to a significant degree during normal transfer operations. It would be desirable to provide an apparatus which is capable of transferring all types of coal (or other friable materials) with a minimum amount of degradation under both ambient and pressurized conditions. The water content of the particulate solids is another factor which must be considered when designing any transport system. Many transport devices which are suitable for transporting completely dry particles do not function properly when the moisture content of the particulate material is raised. The same is true for particulate metering devices. Conventional metering devices which are designed to measure dry particulates may not be well suited to meter moist solids. It would be desirable to provide a transport apparatus which is capable of moving and/or metering particulate solids regardless of their moisture content under both ambient and pressurized conditions. It is apparent from the above background that there is a present need for a solids handling or pumping device which operates as a single unit to provide simultaneous transport and metering of particulate material in ambient and pressurized conditions. The unit should be capable of transporting and metering a wide variety of particle types under a wide variety of conditions. Further, the unit should be structurally strong, and mechanically simple and durable so that it can be operated continuously over extended periods of time without failure. SUMMARY OF THE DISCLOSURE In accordance with embodiments of the present invention, an apparatus and method is capable of transporting and metering particulate materials with increased inlet flow efficiency and reliability, with improved drive force and/or against a gas or fluid pressure head. Solids pumps according to embodiments of the present invention are particularly suitable for transporting a wide range of particulate materials, including both small and large particulates and mixtures of particulates, having varying degrees of moisture content. According to embodiments of the present invention, particulate material enters a transport duct located adjacent at least one, and preferably between two, drive walls (such as, but not limited to, the facing walls of two parallel, opposed disks) . Movement of the drive wall(s) from an inlet towards an outlet causes the particles of the particulate material to interlock with each other, with the outermost particles engaging the drive wall(s), such that drive force is transferred from the drive wall(s) to the particles. In accordance with various embodiments of the present invention, the inlet to the transport duct is improved so as to minimize or avoid the occurrence of the drive wall(s) thrusting particles into a dead region, in which the movement of the particles is slowed or stopped. According to one embodiment, the improved inlet is provided with a shroud plate adjacent to each of two drive walls. Each shroud plate is positioned adjacent a respective drive wall, so as to provide a barrier, inhibiting contact between the drive wall and the particulate material at locations on the drive wall which would otherwise tend to thrust the particles toward a dead region. In a further embodiment, the improved inlet is provided with an abutment wall shaped so as to minimize or avoid the formation of a dead region. In another embodiment, the improved inlet is provided with a stationary wall, opposite the abutment wall, which is shaped so as to minimize or avoid the formation of a dead region. In yet another embodiment, the improved inlet is provided with a particle propelling device (such as a driven paddle wheel structure, a drive roller, a vibrator, a pneumatic blower device or the like) for imparting an additional positive force on the particles (directed toward the drive duct of the apparatus) in the zone in which a dead region would otherwise be formed. Further embodiments employ a combination of some or all of the above embodiments to provide an improved inlet. In preferred embodiments, particulate material is compacted or compressed within the transport duct sufficiently to cause the formation of a transient solid or bridges composed of substantially interlocking particulates spanning the width of a transport duct. Successive bridges occur cumulatively within the transport duct as further particulate material enters the inlet. For certain particulate materials, this cumulative bridging may occur without the use of chokes or dynamic relative disk motion. However, further embodiments may include chokes or dynamic relative disk motion. Examples of such chokes and disk motions are described in U.S. Patent No. 5,051,041; U.S. Patent No. 4,988,239 and U.S. Patent Application No. 07/929,880 (each of which are assigned or licensed to the assignee of the present application and each of which are incorporated herein by reference) . In various embodiments, the transient solid of interlocked particulates forms a barrier against the pressure head, to inhibit a pressure blow-back through the pump, from the outlet side toward the inlet side. Thus, embodiments of the present invention relate to a transport duct type particulate solids pumping system with an improved ability to pump against a gas or fluid pressure head. As a result of extensive research and development efforts focussed on higher gas or fluid pressure operations (operations in which the gas or fluid pressure on the output side of the pump is greater than that on the input side of the pump) , the inventor has recognized that a number of factors contribute to higher pressure pumping capabilities. This has led to developments, described herein, by which any one or combination of these factors can be affected to improve the ability of a particulate materials pumping system to pump against a gas or fluid pressure head. For example, the ability of the drive surface to transfer drive force to the moving mass of particles, the ability to inhibit the portion of the transport duct adjacent the drive surface from becoming pressurized, the configuration and length of the duct, each have been found to contribute to the ability of the apparatus to pump against a gas or fluid pressure head. Thus, various embodiments of the invention provide means for improving the transfer of drive force to the particles. Further embodiments provide means for inhibiting pressurization of the transport duct, and further embodiments provide apparatus dimensions and configurations for improved pressure operations. According to one embodiment for improving the transfer of drive force, the moving drive surface (or surfaces) has at least one discontinuity having a downstream facing drive surface. The discontinuity defines a transport facilitation zone which improves the ability of the drive surface to interlock with the interlocked particulates of the transient solid. In further embodiments a plurality of discontinuities, such as a plurality of evenly spaced discontinuities, are provided on the drive surface. The improved interlocking of the transient solid with the drive surface, in turn improves the ability of the particulates forming the transient solids to bridge. The improved bridging results in an improved pressure barrier formed by the bridged particulates. According to further embodiments of the invention, the shape and dimension of the outlet duct is designed to retain a moving mass of particles therein during the pumping operation, such that the moving mass of particles function as a dynamic plug against gas or fluid pressure on the outlet side of the apparatus. Further embodiments employ venting means by which pressure may ve vented from the outlet duct or the drive channel. The uniform and constant flow rate provided by the apparatus and method in accordance with embodiments of the present invention is particularly well suited for both transporting and metering particulate material under a variety of conditions. The volume of particulate material being delivered is conveniently and accurately determined by measuring the rotational speed of the disks and relating this to the cross-sectional area of the duct. During metering operations, conventional monitoring equipment may be included to ensure that the passageway is full of solids during the metering process. The above discussed and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of a prior art solids pump, with one disk removed, so as to show the pump interior; FIG. 2 is a schematic side view of a preferred exemplary apparatus, with one disk removed so as to show the pump interior and an embodiment of a preferred exemplary inlet provided with shroud plates between opposing interior surfaces of parallel rotary disks; FIG. 3 is a perspective cut away view of the drive rotor of the preferred exemplary apparatus shown in FIG. 2, showing an embodiment of a preferred exemplary shroud plate assembly provided between parallel rotary disks; FIG. 4 is a partial sectional side view of a preferred exemplary apparatus, showing an embodiment of a preferred exemplary inlet in accordance with another embodiment of the present invention; FIG. 5 is a perspective cut away view of the drive rotor of the preferred exemplary apparatus shown in FIG. 4 showing an embodiment of a preferred exemplary shroud plate assembly provided between parallel rotary disks; FIG. 6 is a schematic side view of yet another preferred exemplary apparatus, with one disk removed so as to show the pump interior and an embodiment of a preferred exemplary inlet duct and shroud plate assembly provided adjacent the inlet between opposing interior surfaces of parallel rotary disks; FIG. 7 is a schematic side view of a further preferred exemplary apparatus, with one disk removed so as to show the pump interior and an embodiment of a preferred exemplary positive motion device, comprising a paddle wheel device provided adjacent the inlet; FIG. 8 is a schematic plan top view of yet a further preferred exemplary apparatus showing an embodiment of a preferred exemplary inlet duct; and FIG. 9 is a schematic side view of another preferred exemplary apparatus, with one disk removed so as to show the pump interior and an embodiment of a preferred exemplary inlet duct configuration. FIG. 10 is a partial sectional transverse view of the drive rotor shown in FIG. 5 showing particulates bridged between opposing interior faces of the rotary disks. FIG. 11 is a plan view of further preferred exemplary rotary disk. FIG. 12 is a partial sectional transverse view of the rotary disk shown in FIG. 11 taken in the 12-12 plane. FIGs. 13 and 14 schematically illustrate dimensions of rotary disks and a primary transport channel. FIGs. 15 and 16 schematically illustrate rotary disks with hubs having different diameters. FIGs. 17 and 18 schematically illustrate rotary disks defining different channel heights. FIG. 19 is a partial sectional side view of a further preferred exemplary apparatus, with an improved ability to pump against gas or fluid pressure, in accordance with another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description is of the best presently contemplated mode of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating general principles of embodiments of the invention. The scope of the invention is best defined by the appended claims. In accordance with preferred embodiments of the present invention, apparatus and methods for transporting and metering particulate materials are provided with an improvements relating inlet flow efficiency and reliability, improved drive force (e.g., to pump against a resistance with increased efficiency and reliability) and/or pumping against a gas or fluid pressure head. The inventor has recognized that a number of factors contribute to higher efficiency pumping and the ability to pump into a pressurized environment (wherein the gas or fluid pressure on the output side of the pump is greater than that on the input side of the pump) . This has led to developments, described herein, by which any one or combination of these factors can be affected to improve the ability of a particulate materials pumping system to pump against a gas or fluid pressure head, or to more efficiently pump into ambient or negative pressure environments. Embodiments may be used for transporting a wide range of particulate materials, including both small and large particulate and mixtures of particulates, having varying degrees of moisture content, under both ambient and pressurized conditions. Various embodiments of the invention are discussed below with respect to rotary disk type structures, wherein two spaced apart, opposing walls of a pair of parallel, rotary disks form drive walls, with a transport duct or channel therebetween. However, it will be recognized that further embodiments of the invention may be operable with, or provided with, drive walls formed from structures other than rotary disks, such as spaced moveable walls which move in a generally linear manner and define a transport duct or channel therebetween. Apparatus according to an embodiment of the present invention is shown generally at 30 in FIG. 2. The apparatus 30 includes a housing (not shown) , a drive rotor or rotary disk assembly 31, an inlet 32 and an outlet 34. A transport duct or channel 36 extends between the inlet 32 and the outlet 34. The rotary disk assembly 31 has two opposing rotary disks 37 (one of which is removed from the figure so as to show the interior of the apparatus) . The disk assembly 31 may be coupled to any suitable drive system, such as, but not limited to a hydrostatic or electrically-driven motor (not shown) , for rotating the disks 37 in the direction of arrow 33. The transport duct 36 is formed between substantially opposed faces of the two rotary disks 37. As shown in Fig. 2, the transport duct 36 is further defined by at least one arcuate wall 35 extending between the inlet 32 and the outlet 34. Preferably, the arcuate wall 35 is stationary relative to the housing and may even be formed as part of the housing. As the disks 37 are rotated, the disk faces provide drive walls or surfaces along the transport duct which move relative to the housing in the direction from the inlet 32 towards the outlet 34. As discussed above, other embodiments may employ drive walls formed from opposing faces of other types of moving walls, e.g., other than rotary disks. Referring to Fig. 2, the transport duct 36 has a first section 38 between the two rotary disks 37 below the inlet 32 where particulate solids 40 fed through the inlet 32 are introduced into the transport duct 36. As discussed above with respect to Fig. 1, prior to improvements as set forth herein, some of the particles entering the first section 38 of the transport duct 36 would be thrusted or forced into a dead region, wherein a mass of slow moving or stopped particles would accumulate. However, embodiments of the present invention are provided with improved inlets capable of minimizing or avoiding the creation of such a mass of particles in a dead region. According to one embodiment, best shown in Figs. 2 and 3, a shroud plate assembly 42 is provided at the first section 38 between the two rotary disks 37. The shroud plate assembly 42 comprises two plate members positioned between the two rotary disks 37, with each plate member covering a portion of the surface of a respective disk 37, adjacent the first section 38 of the transport channel 36. As a result, the particulate solids 40 introduced into the first section 38 (between the two plate members of the shroud plate assembly 42) are substantially inhibited by the shroud plate assembly from contacting the drive surfaces of the rotary disks 37 within section 38. Consequently, with the shroud plate assembly 42 in place, the tangential thrust or force which the disk drive surfaces would otherwise impart on the particulates 40 in the first section 38, does not act on the particulates. In this regard, depending upon its shape and position, the shroud plate assembly 42 can minimize, or even eliminate, the tangential thrust which would otherwise move the particulate solids 40 adjacent the periphery of the rotary disks 37 toward a stationary wall 43 of the inlet 32. As a result, the particulate solids 40 flow smoothly through the inlet 32, between the plate members of the shroud plate assembly 42. It is noted that the particulate solids 40 moving through the shroud plate assembly 42 come in contact with the surfaces of the rotary disks 37 at different radii of the rotary disks 37 and at different angles with respect to the direction of rotation along the bottom end 44 of the shroud plate assembly 42. It has been found that the separation h between the bottom end 44 of the shroud plate assembly 42 and a hub 46 affects the uniformity and consistency of the flow of particulate solids 40 through the inlet 32 and the transport duct 36. In addition, the position of the shroud plate assembly 42 with respect to the transport channel 36 and the shape of the shroud plate assembly 42 which cover the surfaces of the rotary disks 37 affect the radial position (relative to the disks) at which particles exit the shroud plate assembly. Preferably, the separation h and the position and shape of the shroud plate assembly 42 are selected for optimum flow. The selection of these parameters depends upon the type of materials being transported and the environmental conditions under which the transportation would take place. In the Fig. 2 embodiment, the shroud plate assembly 42 is fixed to the bottom end portion of the inlet 32. In alternative embodiments, the shroud plate assembly and the inlet may be formed as one integral unit. Furthermore, the shroud plate assembly may be fixed to structural members other than the inlet. In one embodiment, the shroud plate assembly is coupled to a hopper for storing particulate solids therein which is arranged to supply particulate solids to the inlet of the apparatus. In further embodiments, a hopper may have a vibrating means to facilitate feeding of particulate solids out of the hopper. The shroud plate assembly, in such embodiments, may be coupled to the vibrating means to further facilitate the flow of particulate solids. Apparatus according to another embodiment of the present invention is shown generally at 50 in FIG. 4. The apparatus 50 includes a housing 52, an inlet duct 54 and an outlet duct 56. A drive disk assembly 58 is rotatably mounted within the housing 52, on a shaft 60 for rotation about the axis of the shaft 60. Any suitable drive device, such as, but not limited to a hydrostatic or electrically-driven motor (not shown) , may be operatively coupled to the drive disk assembly 58 (e.g., through the shaft 60) for rotatably driving the rotor in the direction of arrow 64 in FIG. 4. As best shown in FIG. 5, the drive rotor or disk assembly 58 includes a pair of rotary disks 66 and 68, each having an inner diameter 70 and an outer diameter 72. The disk drive assembly 58 further includes a hub 74. Preferably, the disks of the drive disk assembly are separable in order to allow access to the interior of the pump apparatus and to facilitate servicing or replacement of parts of the apparatus. The rotary disks 66 and 68 include opposing interior faces 76 and 78. The opposing interior faces 76 and 78 may be planar or include a plurality of discontinuities 89 as described below. Such surface discontinuities on the drive walls can improve the transmission of drive force to the particulate material, which can result in a further improved ability to pump against a pressure head. The preferred exemplary apparatus 50 includes one or more exterior shoes such as those shown in FIG. 4 at 90 and 92. In further embodiments, a single stationary wall, such as discussed above with respect to wall 35 in Fig. 2, may be employed as an alternative to plural shoes. The exterior shoes 90 and 92 are designed to close the transport duct formed between disk faces 76 and 78. Each of the exterior shoes 90 and 92 includes a stationary inner wall 94 and 96, respectively. Inner walls 94 and 96, in combination with the hub 74 and opposing interior faces 76 and 78, define the transport duct 100 and, thus, the boundary of the cross-sectional area of the duct at any given point along the length of the duct from the inlet to the outlet. ' Both exterior shoes 90 and 92 are mounted to the housing by way of suitable mounting brackets or pins. Preferably, the inner wall, or inner walls in the case of plural shoes, are accurately formed so as to conform to the circular perimeter of the rotary disks 66 and 68. In one preferred embodiment, the inner wall of the shoe extends axially (transversely of the shoe) beyond interior surfaces 76 and 78, respectively, of the drive rotor 58 so as to overlap the interior surfaces 76 and 78 of the drive rotor. The shoe is placed as close as possible, within acceptable tolerances (dependent upon, e.g., the type and particle size of the material being transported) , to the outer diameters 72 of interior faces 76 and 78. In the Fig. 4 configuration, the shoe is not radially adjustable to move closer or further away from the hub 74 of the drive rotor 58 to change the cross-sectional area of the primary transport channel 100. In an alternative embodiment, the shoe is sized and shaped so as to fit between opposing interior faces 76 and 78 to form a curved outer wall for the primary transport channel 100. In this configuration, the radial location of the shoe may be adjusted toward or away from the hub 74 of the drive rotor 58 so as to change the cross-sectional area of the primary transport duct 100 and to select the general configuration of the duct as one of a generally diverging duct, converging duct or constant cross- sectional area duct. For this purpose, a screw adjuster may be connected to one or a plurality of shoes, for example, of the type shown in U.S. Patent No. 4,988,239. The inward and outward adjustment of shoe allows setting up a choking or compaction of the solids as they move through the pump or, alternatively, to provide a diverging or a constant cross-sectional area along the duct. In a further embodiment of the present invention, convergence or divergence of the cross-sectional area of the duct 100 and/or compaction of particulate solids is accomplished by positioning rotary disk 66 at an angle relative to rotary disk 68 such that the distance between the opposing interior faces 76 and 78 adjacent the inlet duct 54 is different than the distance between opposing interior faces 76 and 78 between inlet 54 and outlet 56. In further embodiments, the angle at which the rotary disks rotates relative to each other may be adjusted. Variation of the angle modifies the rate of change of the cross-sectional area between the inlet and the outlet to provide a different convergence or choke or divergence in the duct. Various aspects of the foregoing angled disk embodiments and preferred arrangements for accomplishing the same are more fully described in U.S. Patent Application Serial No. 07/929,880 (assigned to the assignee of the present invention and incorporated herein by this reference) . Apparatus 50 further includes a shroud plate assembly 102 provided adjacent the inlet 54 between the two rotary disks 66 and 68. As best shown in Fig. 5, the shroud plate assembly 102 comprises a pair of plate members 104 which oppose and cover the drive surfaces of the two rotary disks 66 and 68 adjacent the inlet 54. Each plate member 104 is arranged adjacent a respective disk 66 or 68 and terminates at a bottom end 106 in an initial feed area 108 of the primary transport duct or channel 100. The initial feed area 108 may be generally defined as being between the inlet 54 and the portion of the hub 74 facing the inlet and between the two rotary disks 66 and 68. As with the shroud plate assembly 42 discussed above, the shroud plate assembly 102 operates to substantially inhibit the particulate solids 91 introduced into the initial feed area 108 from contacting portions of the surfaces of the rotary disks 66 and 68. The shroud plate assembly 102, thus, minimizes or eliminates the tangential thrust which would otherwise move the particulate solids 91 adjacent the periphery of the rotary disks 66 and 68 toward a choke side wall 110 of the inlet 54 to form a mass of slow moving or stopped particles (a dead region) . Because the particulate solids 91 moving through the shroud plate assembly 102 come in contact with the surfaces of the rotary disks 37 at various radii relative to the disks 66 and 68 and at different angles with respect to the direction of rotation along the bottom end 106 of the shroud plate assembly 102, further improvements in achieving a uniform consistent flow of the particulate solids may be provided by selecting the configuration of the shroud plate assembly 102, including the angle of the bottom edge 106 of the shroud plate assembly relative to the direction of motion of the disks. The angle and shape of the bottom edge 106 determines at which radius along the drive disks the particles flowing out of any given location along the bottom edge 106 exit the shroud plate assembly. The size of the drive rotor 58 may vary widely, depending upon the type and volume of material which is to be transported or metered. Typically, outside diameters for the rotary disks 66 and 68 may range from a few inches to many feet. The smaller rotary disks are well suited for use in transporting and metering relatively small volumes of solid material such as food additives and pharmaceuticals. The larger size disks may be utilized for transporting and metering large amounts of both organic and inorganic solid materials, including food stuffs, coal, gravel and the like. The apparatus is equally well suited for transporting and metering large and small particles and mixtures of them, and may be used to transport and meter both wet and dry particulate material. Apparatus according to a further embodiment of the present invention is shown generally at 130 in Fig. 6. The apparatus 130 includes a multiple column inlet duct assembly 132 which also defines a shroud assembly. The assembly 132 is located between a pair of rotary disks 134 which rotate in the direction of an arrow 135. The assembly 132 may be adapted to feed one type of particulate material or a plurality of different types of particulate materials (a different material in each column) simultaneously into the transport duct or channel of the pump. To improve the ability to provide a uniform, consistent flow of particulate solids through the apparatus 130, the multiple inlet duct assembly 132 includes multiple inlet duct columns 132a to 132d, each having walls (functioning as shroud plates as discussed above) adjacent a portion of the disks 134. The columns 132a to 132d terminate at mutually different radii along the rotary disks 134. In one embodiment of the present invention, the inlet duct column 132a located at a choke side 136 terminates adjacent the periphery of the rotary disks 134 and the inlet duct column 132d located at an abutment side 138 terminates adjacent a hub 140. The inlet duct column 132b extends deeper into the space between the rotary disks 134 than the inlet duct column 132a, and the inlet duct column 132c extend deeper than the inlet duct column 132b but shallower than the inlet duct column 132d. The configuration of the inlet duct assembly 132, including the individual duct lengths and cross-sectional sizes may be selected to provide a desired flow rate for each columnar duct. Apparatus according to yet a further embodiment of the present invention is shown generally at 150 in Fig. 7. The apparatus 130 includes an inlet 152, an outlet 153 and a pair of rotary disks 154 which rotate in the direction of an arrow 155. To inhibit the formation of a dead region adjacent the inlet 152, the Fig. 7 embodiment includes a propelling device or propelling means for applying a further positive force (directed toward the transport duct or channel of the device) on any particles which may begin to accumulate in the region that would otherwise become a dead region. In the Fig. 7 embodiment, the means for applying a further positive force comprises a paddle wheel 156. The paddle wheel 156 may be driven by any one of suitable driving means, such as a motor (not shown) . During the pump operation, particulate solids moved toward the choke side 158 by the tangential thrust of the disks are positively pushed by the paddle wheel into the primary transport duct 160. Preferably, the rotational speed of the paddle wheel 156 is adjusted to achieve a uniform, consistent flow of particulate solids through the inlet 152 and the primary transport duct 160. It will be understood that, while the Fig. 7 embodiment shows a paddle wheel devices as an example of means for applying a further positive force, other embodiments may employ any one or combination of such devices as drive rollers, vibrators, pneumatic devices, gas or fluid blowers, or the like. Apparatus according to another embodiment of the present invention is shown generally at 170 in Fig. 8. The apparatus 170 includes an inlet 172 and a pair of rotary disks 174 which are rotated in the direction of an arrow 175. The inlet 172 has a cross-section configuration designed to minimize or avoid the creation of dead regions at or around the inlet 172, so as to provide a uniform, consistent flow of particulate solids through the inlet and the apparatus 170. In one embodiment, the inlet 172 has a width wl at the outer diameter side (or choke side) 176 substantially larger than a width w2 at the abutment side 178. Preferably, the width wl gradually narrows toward the width w2, which is approximately one third of the width wl. However, other suitable relative dimensions may be selected dependent upon the type of material being transported and the conditions under which the transportation operation is to take place. The illustrated inlet configuration provides a flow rate of particulate solids at the abutment side 178 which is substantially smaller than that at the choke side 176 (due to the cross-sectional area of the inlet 172 on the abutment side being substantially less than that on the choke side. As a result, a lower percentage of the total incoming particles are subjected to the tangential thrust which may otherwise create a dead region. The. likelihood of a dead region being formed is, therefore, reduced. Apparatus according to yet another embodiment of the present invention is shown generally at 190 in Fig. 9. The apparatus 190 includes an inlet 192, an outlet 196 and a pair of rotary disks 194 which rotate in the direction of an arrow 196. A primary transport duct 200 is generally defined between the rotary disks 194 and between the inlet 192 and the outlet 198. In this preferred embodiment, the inlet 192 has a lower section 202 contiguous with the primary transport channel 200 and an upper section 204 which connects to the lower section 202 at the upstream side of the flow of particulate solids. The lower section 202 has a side wall on the outer diameter side (or a choke side wall) 206 and an abutment side wall 208 opposing the choke side wall 206, and located upstream of the choke side wall 206. It has been found that by forming either one or both of the walls 206 and 208 with substantial curved or concave portion where these walls meet or traverse the outer peripheral dimension of the disks, the tendency for particulate material to collect in a dead region can be substantially reduced or eliminated. In one embodiment, the abutment side wall 208 is concave and bows out in the direction opposite to the disk rotation direction 196. In further preferred embodiments, the choke side wall 206 is angled to define a diverging inlet so that the flow of particulate solids moving through the inlet 210 is directed, upon entry into the primary transport duct 200 substantially in the same direction of the flow of particulate solids in the primary transport duct 200. The above discussed abutment and choke side wall configurations have been found to reduce the effect of tangential thrust which may otherwise create a dead region at or adjacent the inlet 210. Referring to Figs. 4 and 5, it is preferred when pumping solids into pressurized systems that the entire cross-sectional area of at least portions of the transport channel 100 and the outlet 56 be filled with solids during pumping. This forms a dam at the pump outlet which is a barrier to possible deleterious effects of reverse flow of gases, liquids or solids back into the pump through the outlet. The cumulative bridging of the particulates provides a sequentially formed cascaded reinforcement which adds strength to the particle bridge portions closer to the outlet, so as to better withstand the higher pressure at the outlet side of the apparatus. The ability of embodiments of the present invention to improve the flow of material through the pump inlet thereby provides an improved ability to maintain the transport channel 100 and outlet 56 filled with solids, and, thus, an improved ability to pump against a pressure head. Furthermore, the ability of drive surfaces to transfer drive force to a moving mass of particles has been found to contribute to the ability of the apparatus to pump against a gas or fluid pressure head. According to one embodiment for improving the transfer of drive force, the moving drive surface (or surfaces) has at least one discontinuity having a downstream facing drive surface. The configuration of undulation(s) (or discontinuities) on the opposed surfaces of the disks may vary from embodiment to embodiment. Preferably, each discontinuity defines a transport facilitation zone which improves the ability of the drive surface to interlock with the interlocked particulates of the transient solid. In further embodiments a plurality of discontinuities, such as a plurality of evenly spaced discontinuities, are provided on the drive surface. For example, the opposing interior faces 76 and 78 of the rotary disks 66 and 68 shown in Fig. 5 are provided with a plurality of evenly spaced radially extending discontinuities 89. Preferably, the discontinuities of opposing interior faces define a symmetric channel for transport of particulates as best shown in FIG. 10. This symmetric configuration mitigates against uneven loadings on the bearing assembly (not shown) supporting drive rotor during compaction and transport of particulates. Each discontinuity 89 defines a transport facilitation zone 254 having a downstream facing drive surface 256, a bottom area 258 and an upstream facing surface 260 (as best shown in Fig. 10) . Referring to Figs. 5 and 10, downstream facing drive surfaces 256 are perpendicular to interior faces 76 and 78 and backwardly curving such that trailing end 264 extends away from outlet (e.g. outlet 56 in Fig. 4) relative leading end 262 as rotary disk 66 (and disk 68) moves between the inlet and outlet. This backwardly curving configuration facilitates discharge of particulate at outlet. In a preferred embodiment shown in FIGS. 5 and 10, the width of transport facilitation zones 254 increase as transport facilitation zones 254 extend from the inner diameter to the outer diameter locations on the disk 66 (and disk 68) . Upstream facing surfaces 260 of each rotary disk incline upwardly from bottom area 258 to the interior face of the rotary disk. The configuration of discontinuities on the opposed interior surfaces 76 and 78 may vary substantially in accordance with the present invention. In a preferred embodiment of rotary disks shown in Figs. 10 and 11, the discontinuities on opposing interior faces 76 and 78 include a plurality of evenly spaced radially extending upraised portions 282, each having a downstream facing drive surface 284 and an upstream facing surface 286 located upstream of the downstream facing drive surface 284, each of which is substantially perpendicular to the interior face of the rotary disk. The upraised portions 282 also include an inner surface 288 and an outer surface 290, both of which are contiguous with a downstream facing drive surface 284 and an upstream facing surface 286 and which are substantially perpendicular to the interior face of the rotary disk. The inner surface 288 is positioned outward of the inner diameter 292 of the rotary disk and is substantially perpendicular to the radial component which intersects therewith. The outer surface 290 is positioned inward of the outer diameter 294 of the rotary disk and is substantially perpendicular to the radial component which intersects therewith. The upraised portion 282 also includes a top surface 296 which is substantially parallel to the interior face of the rotary disk. The width of each top surface 296 expands as the top surface 296 extends from near the inner diameter 292 to near the outer diameter 294 of the rotary disk such that the width of the recess 298 defined by adjacent upraised sections 282 remains constant as the recess 298 extends from near the inner diameter 292 to near the outer diameter 294. The upraised portion 282 is backwardly curving such that the outer surface 290 extends away from outlet relative to inner surface 288 as the rotary disk moves between the inlet and outlet. Alternatively, opposing interior faces may include radially extending undulations defining a wave-like series of alternating crests and troughs. Further embodiments may employ simple ridges or grooves in the disk walls. The improved interlocking of the transient solid with the drive surfaces (e.g., the drive walls having grooves or other discontinuities) , in turn improves the ability of the particulates forming the transient solids to bridge. In particular, the mass of interlocked particles forming the transient solid becomes interlocked with the surface discontinuities in the drive walls, as shown in Fig. 10, which results in an improved transfer of drive force and, therefore, an improved ability of the particulates to bridge. The improved bridging results in an improved pressure barrier formed by the bridged particulates. In various above-described preferred embodiments, the drive force of the drive rotor (31 or 58) is enhanced by providing discontinuities 89 on the opposing interior faces 76 and 78. The drive force of the apparatus may be defined as a pumping capability of the apparatus of driving the particulate solids through the primary transport channel against a predetermined particulate pressure or any kind of predetermined resistances without causing slips of the particulate solids on the opposing interior faces 76 and 78. The resistances may be caused, for example, by gravity, pressurized fluid (gas or liquid) of a pressurized system which is coupled to the outlet of the apparatus, or a combination of both. Further embodiments employ one or a combination of a variety of other features which increase the drive or pumping forces of the apparatus. For example, the stationary inner wall 94 and 96 of each of the exterior shoes 90 and 92 (Fig. 5) may be coated with a low friction material, such as for example, polytetrafluoroethylene, and other ultra-high molecular weight materials, to reduce the friction between particulate solids and the stationary inner wall 94 and 96. As a result of the reduced friction, the drive force is increased. In another embodiment of the present invention, the material of which the interior surfaces 76 and 78 of the rotary disks 66 and 68 are made may be selected from those having an increased coefficient of friction to increase the drive force. In further embodiments, the friction between the drive surfaces 76, 78 and the particulate material may also depend on the smoothness or roughness of the surfaces. Thus, the drive force may be increased by increasing the roughness of the drive surfaces 76 and 78. Alternatively, the material of which the interior surfaces 76 and 78 are made may be selected from those having resilience to improve the ability of the particulates to interlock with the disk walls and to improve the efficiency with which the drive force is transferred to the particulates. In still another embodiment of the present invention, the apparatus may be provided with a divergent outlet duct as shown in Fig. 19. Such a divergent outlet duct has a cross-section which increases in area toward an external opening of the outlet duct. The divergence of the outlet duct tends to reduce the pressure of compressed particulate material on the interior surfaces of the outlet duct toward the external opening thereof. As a result, the frictional resistance between particulate material and the interior surfaces is reduced through the outlet duct, resulting in an improved ability to drive the particulate material. Furthermore, it has been recognized that the drive force generated by an apparatus is dependent upon the length of the primary transport channel (e.g. , the channel between the inlet duct 54 and the outlet duct 56 in Fig. 5) through which the solids move. Typically, the longer the primary transport channel relative to the channel width, the greater the drive force of the apparatus. As shown in Figs. 13 and 14, the primary transport channel 250 has a drive length L through which the particulate solids are moved by the rotation of the drive rotor 18 from the inlet 14 to the outlet 16. The primary transport channel 100 has a height H of the drive surfaces of the rotary disks 66 and 68, and a width W which is defined between the opposed faces 76 and 78 of the rotary disks 66 and 68. The hub 74 has a diameter D. The cross-section of the primary transport channel 100 may be of any suitable shape. In the illustrated embodiments, the cross-section shape of the channel 100 is generally rectangular and square. With a rotary disk apparatus, the drive length L is dependent upon the diameter D of the hub 74, such that an increase in the diameter D of the hub 74 results in an increase the drive length L of the primary transport channel 100. This results in an increase in the channel length L to channel width W ratio and, therefore, an increase in the particle drive force generated by the apparatus. It has also been recognized that the drive force generated by an apparatus is further dependent upon the relative dimensions of the drive length L (which in rotary disk systems is dependent upon the hub diameter D) , the height H and the width W of the primary transport channel 100. In particular, it has been found that the drive force is related to (and proportional to) the ratio of the drive length L (or diameter D) to the width W of a primary transport channel of square cross-section (e.g., H = W) . That is, as the ratio of L (or D) to W increases, the drive force increases. It has also been found that, for other than square cross-section shaped channels 100 (e.g., H is not equal to W) , the drive force is not only related to the ratio of L (or D) to W, but is also related to (and proportional to) H. That is, as H decreases, the drive force decreases. This feature is exemplified with reference to Figs. 15 and 16. As shown in Fig. 15, the primary transport channel 100 has the height H and the width W which are equal (e.g. , the shape of the cross-section of the channel is a square) . The hub has the diameter Dl which define a drive length LI. In Fig. 16, the height H and the width W of the primary transport channel 100 are the same as in Fig. 16. In other words, the cross- section of the primary transport channel 100 is the same in Figs. 15 and 16. However, the diameter of the hub in Fig. 16 is more than twice that of Fig. 15. The drive length of the primary transport channel 100 in Fig. 16 is L2, which is more than twice that of Fig. 15. Accordingly, the ratio of the diameter D of the hub to the width W of the primary transport channel for the Fig. 15 embodiment is Dl/W, and for the Fig. 16 embodiment is D2/W, wherein D2/W is more than twice the value of Dl/W. As a result, the apparatus of Fig. 16 can produce a substantially greater drive force (or a substantially greater pumping capability against a resistance) than the apparatus of Fig. 15. Furthermore, as shown in Fig. 17, the primary transport channel 100 has a width W which is equal to the width of the channel 100 in Fig. 18. The hub has the diameter D in Fig. 17 is also equal to the hub diameter D in Fig. 18. In Fig. 17, however, the height HI of the drive surfaces defining the primary transport channel 100 are greater than the height H2 in Fig. 18. As a result, the apparatus of Fig. 17 can produce a greater drive force (or a greater pumping capability against a resistance) than the apparatus of Fig. 18. Thus, from the forgoing, it can be seen that the magnitude of the drive force is dependent on at least one of the ratio of the drive length L to the width W (L/W) , the ratio of the diameter D of the hub to the width W (D/W) and the ratio of the drive length L to the cross-section area S of the transport channel (L/S) . More particularly, it is recognized that the greater the L/W ratio, or the D/W ratio, or the L/S ratio, the greater the drive force of the apparatus. In addition, the greater the height H, the greater the drive force of the apparatus. Therefore it is appreciated that the magnitude of the drive force F of an apparatus may be characterized as a function of each of the L/W ratio, the D/W ratio, the L/S ratio, and the height H, e.g., by the following formulae: F = f(L/W); F = f(D/W); F = f(L/S); or F = f(H). It is often the case that the drive force F required for a particular application (e.g., pumping material up an incline or vertically upward, pumping against a pressure head and/or pumping over a predetermined distance) can be determined from various parameters of the application (e.g., the angle of incline, the magnitude of pressure and/or the length of the distance over which the pumped material is to travel) . Therefore, according to embodiments of the invention, the values of any one or combination of L, D, W, S, and H are selected so as to provide a drive force F suitable for a particular application. Preferably, the drive force value F of the apparatus is greater than a total pumping pressure P including a pressure of particulate solids, an external fluid (gas or liquid) pressure for cases wherein the apparatus is pumping into a pressurized system, and other resistances so that the apparatus effectively drives particulate materials without causing the particulate solids to slip on the faces of the rotary disks. Accordingly, the following relations may be established: F > P; or f(L/W) > P; or f(D/W) > P; f(L/S) > P; or f(H) > P. Therefore, according to embodiments of the invention, the values of any one or combination of L, D, W, S, and H are selected so as to provide a drive force F greater than P. The orientation and configuration of the output duct of the pump also affects the ability to transfer particulate solids into higher pressure on the output side relative to the input side. For example, further improvements in the ability and efficiency of operation for pumping into pressurized systems are achievable with the an upwardly facing outlet duct, such as shown at 302 in the apparatus 300 in Fig. 19 (the same reference numerals are used for elements similar to those used in the apparatus shown in Fig. 4) . An end portion 304 of the outlet duct 302 is coupled to a pressurized system 306. Preferably, the outlet duct 302 faces upward (i.e., the end of the outlet duct coupled to the pump is lower than the opposite end of the outlet duct) so that particulate material is driven upward before being discharged from the outlet duct 302 into the pressurized system 306. As a result of the upward directed wall or walls of outlet duct 302, the duct, in effect, forms a receptacle which holds particulate material as the particulate material is moved through the outlet duct. The moving particulate material held within the walls of the outlet duct at any instant during the pumping operation is acted upon by the drive force of the pump, as additional particulate material is driven into the lower end of the outlet duct. At the same time, gravity and gas or fluid pressure on the outlet side acts on the particulate material held within the outlet duct walls. The moving particulate material held within the outlet duct at any given instant during the pumping operation is, therefore, compacted and tends to fill the outlet duct interior. As a result, the particulate material forms, in effect, a moving or dynamic plug which inhibits the passage of gas or liquid into the drive duct of the pump from the outlet side. Furthermore, greater compaction or compression tends to occur toward the lower end of the outlet duct (i.e., nearer to the drive duct), which tends to further strengthen the particulate bridge portions in the primary transfer channel or drive duct 100, which in turn tends to increase the ability of the pump to transfer drive force to the transient mass. As a result of this cumulative affect outlet duct 302, the overall system can operate against a significantly higher pressure on the outlet side of the pump relative to the inlet side of the pump. This cumulative affect is further enhanced by such drive force improvement features as discussed above (e.g., with respect to embodiments of drive walls having discontinuities and transportation duct dimension ratios) . That is, the improved ability to transfer drive force results in an improved bridging and an improved transfer of particulate material into the outlet duct, which, in turn, results in an improved dynamic plug and, thus, a further improved ability to pump against pressure. Thus, the improved ability to transfer drive force to the particulate material and the improved outlet duct configuration and/or orientation cooperate with each other in a cumulative and synergistic manner to provide a greatly improved apparatus for pumping against pressure. In preferred embodiments, the outlet duct 302 has an outwardly diverging cross-section (diverges in the direction from the end coupled to the transfer channel or drive duct 100 toward the end 304 coupled to the pressurized system 306) . Because the cross-section of the outlet duct 302 gradually diverges toward the end portion 304, the particulates become less compacted toward the end portion 304 of the outlet duct 302. As a result, the force of the particulate on the internal surface of the outlet duct wall 305, and therefore the friction between the particulate material and the wall 305, reduces toward the outlet duct end portion 304. As a consequence, while the capacity to withstand the higher pressure is improved by the upwardly facing outlet 302, the drive force of the apparatus 300 for driving the particulate matter through the outlet duct need not be substantially increased. The length of the outlet duct 302 is preferably designed such that a sufficient amount material will be held in the outlet duct 302 at any instant during the pumping operation, to support and withstand the higher pressure. Since particulate material which is carried through the outlet duct 302 exerts pressure on the internal surface of the wall 305, the internal surface of the wall 305 should preferably be coated, to reduce friction between particulate material and the wall 305, with a low friction material, such as for example, polytetrafluoroethylene, and other ultra-high molecular weight materials. Alternatively, the drive force of the apparatus 300 may be increased so that the particulate material can be moved against greater frictional resistances at the upwardly facing outlet. As a result, a stronger cascaded reinforcement of particulate material may be formed to withstand higher pressures of the pressurized system. As apparent from the above discussion, the shape and orientation of the outlet duct 302 can have dramatic affects on the ability and efficiency of the apparatus to move particulate material against a pressure head, including a gas or fluid pressure head. Accordingly, the shape and orientation of the outlet duct is preferably selected to provide the optimal pressure handling capabilities for a particular pumping operation. It has been found that further improvements in the ability to operate against a gas or fluid pressure head are achieved by inhibiting the drive duct or channel from becoming pressurized (containing a greater gas or fluid pressure than the pressure on the inlet side of the apparatus) . Accordingly, further embodiments of the invention provide for the minimization of pressure leakage from the higher pressure outlet side of the apparatus into the drive duct or channel 100. Venting of pressure at various locations along the outlet duct and/or the drive channel or duct may minimize or inhibit the pressurization of the drive channel or duct 100. Examples of such venting arrangements are discussed below. According to a further embodiment, the apparatus 300 is provided with a non-return valve system for preventing pressurized gas or fluid of the pressurized system 306 from entering into the apparatus 300 when the apparatus 300 runs short or out of particulate material to pump out. For example, in a preferred embodiment, a valve plate 308, pivotal about a pin 310, is provided adjacent the external end portion 304 of the outlet 302. Particulate material being discharged from the outlet 302 pushes against the valve plate 308 to open the valve plate 308 during a normal pumping operation. On the other hand, when the apparatus 300 runs short or out of particulate material, the valve plate 308 closes the outlet 302 to inhibit the pressurized gas or fluid from entering into the primary transport channel 100 of the apparatus 300. In another embodiment, pressure sensor devices (not shown) may be provided to monitor the pressure in the ' primary transport channel 100 and/or in the outlet duct 302. Monitored pressure may be used to control a servo-motor system or other suitable motor (not shown) coupled to the valve plate 308 for opening and closing of the valve plate 308 so that the pressurized gas or fluid does not enter into the primary transport channel 100 when the apparatus runs out of particulate material. As discussed above, particulate solids are substantially compacted in the outlet 302 during pumping, and form a sequentially moving cascaded bridging of particulate solids or a moving dynamic plug through the outlet 302 to act as a seal (or partial seal) against the pressurized fluid of the pressurized system 306. However, the fluid, gas or liquid, may still be able to seep through minute paths formed between particulate solids, and possibly into the inlet 54. As mentioned above, to inhibit or prevent the fluid from seeping into the inlet 54, the apparatus 300 may be provided with a vent system for venting fluid pressure. For example, as shown in Fig. 19, a vent 311 is provided in the outlet 302 adjacent the primary transport channel 100 (the vent 311 may be arranged closer to the channel 100 than as shown in Fig. 19) , or on the housing or shoes adjacent the periphery of the rotary disks 66 and 68. The vent 311 may be coupled to a pump device (not shown) to pump out the fluid seeping through the particulate solids. Alternatively, the pressure of the fluid itself may be enough to operate the vent. Preferably, the vent 311 is provided with a valve 312 for selectively closing or opening the vent 311. The vent system may be provided at any suitable location along the primary channel 100. For example, a vent may be provided at the exterior shoe 92, or at an abutment member 314. In further preferred embodiments, gaps between the disks and the housing, shoes or the hub may provide suitable venting outlets. The length of the transport duct 100 is preferably designed such that a sufficient amount of cumulative, cascaded bridging occurs in the duct to support and withstand the higher pressure at the outlet side of the pump. This can be accomplished with a convergent duct, constant cross-section duct or divergent duct system. A divergent duct system (wherein the primary drive duct diverges from the inlet toward the outlet) may be beneficial for pumping into a pressurized system. In particular, the divergent duct 100 would, in effect, be converging in the direction from the outlet toward the inlet, which would inhibit any movement of the transported mass of particulate material backwards through the pump (in the direction toward the inlet) by back-pressure forces. Furthermore, the ability to inhibit pressurization of the transport duct in the apparatus has been found to contribute to the ability of the apparatus to pump against a gas or fluid pressure head. Thus, various embodiments of the invention provide means for inhibiting pressurization of the transport duct, and further embodiments provide apparatus dimensions and configurations for improved pressure operations. In order to preclude particulates and particulate dust from wedging in the space defined between the housing 52 and the outer edge of each rotary disk 66 and 68, the rotary disks include a chamfer 72 as best shown in FIG. 12 which inclines away from housing 52 as the outer edge extends outward from the interior face of the rotary disk. Preferably, the outer edge is chamfered at an angle of about 45 degrees. A dust drain 74 with an associated valve 76 is provided at the bottom of the housing for allowing removal of dust which may accumulate during pump operation (Fig. 19) . The valve 76 may be left open during pump operation to continually remove dust as it falls into the drain through an interior collection channel (not shown) . Alternatively, the valve 76 may be left closed, and only opened when the interior collection channel has filled with dust. The opening and closing of the valve 76 will, of course, depend upon the dustiness or friability of the particular solid material being transported. The opening and closing of the valve 76 may be performed at the user's preference. The size of the drive rotor may vary widely, depending upon the type and volume of material which is to be transported or metered. Typically, outside diameters for the rotary disks 66 and 68 may range from a few inches to many feet. The smaller rotary disks are well suited for use in transporting and metering relatively small volumes of solid material such as food additives and.pharmaceuticals. The larger size disks may be utilized for transporting and metering large amounts of both organic and inorganic solid materials, including food stuffs, coal, gravel and the like. The apparatus is well suited for transporting and metering large and small particles and mixtures of them, and large and small volumes, and may be used to transport and meter both wet and dry particulate material with the only limitation being that the material cannot be so wet that viscous forces dominate so as to disturb bridging. Although the preferred exemplary embodiments have been shown utilizing a single drive rotor, it is also possible to provide transport apparatus having multiple drive rotors which receive material from a single or multiple inlets. The use of multiple drive rotors provides for increased material through-put without having to increase the diameter of the rotor disk. The bridging of solids results in a positive displacement of the solids. Accordingly, the pump may be used both as a transport and metering device. Due to the positive displacement of solids through the pump, metering is accomplished by measuring the rate of rotation of the drive rotor and calculating the amount of solids flow through the pump based upon the cross-sectional area of the duct. When used as a metering pump, it is desirable that some type of conventional detection device be utilized to ensure that the passageway remains full of solids at all times during solids metering. Such conventional detection devices include gamma ray and electro-mechanical detectors. These detectors are all well known in the art and are neither shown in the drawings nor described in detail. The apparatus elements are preferably made of high strength steel or other suitable material. The interior surfaces of drive disks and the interior walls of the shoes are preferably made of an abrasion-resistant metal or other suitable material having non-adhesive qualities to facilitate discharge at the outlet during operation and to facilitate cleaning during maintenance. In suitable applications, the interior surfaces of the rotary disks and the interior wall of the shoes may be composed of a low friction material, such as polytetrafluoroethylene. Having thus described exemplary embodiments of the present invention, it should be understood by those skilled in the art that the above disclosures are exemplary only and that various other alternatives, adaptations and modifications may be made within the scope of the present invention. For example, although a drive rotor is a preferred form of a moving surface, it is not essential. Any type of movable surface, conveyor belt or other system may be utilized so long as the bridging and a downstream facing drive surface features are provided. The presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

Claims: WHAT IS CLAIMED ISt 1. An apparatus for transporting particulate material against a fluid pressure comprising: a first moveable surface defining a transport channel, an inlet and an outlet, said transport channel located between said inlet and said outlet, the first moving surface operable to move from said inlet towards said outlet; an outlet duct defining a receptacle for holding, during the operation of the apparatus, a mass of the particulate material being transferred by the apparatus, so as to form a moving dynamic plug for inhibiting fluid from entering the primary transport channel from the outlet duct. 2. An apparatus for transporting particulate material according to claim 1, further comprising drive means for moving said first moveable surface between said inlet and said outlet towards said outlet. 3. An apparatus for transporting particulate material according to claim 1, wherein said outlet duct has a diverging cross-section. 4. An apparatus for transporting particulate material according to claim 1, wherein said outlet duct has a bottom end portion adjacent said transport channel, an external end portion opposed to said bottom end portion, and an upwardly inclined internal wall. 5. An apparatus for transporting particulate material according to claim 4, wherein said internal wall of said divergent receptacle defines a divergent receptacle having a cross-section which diverges in the direction away from said transport channel. 6. An apparatus for transporting particulate material according to claim 1, wherein said outlet duct has an internal wall defining a divergent receptacle having a cross-section which diverges in the direction away from said transport channel. 7. An apparatus for transporting particulate material according to claim 1, wherein the outlet duct is coupled to the transport channel at an outlet junction, the apparatus further comprising a pressure vent provided adjacent the outlet junction. 8. An apparatus for transporting particulate material according to claim 1 further comprising a pressure vent in said transport channel. 9. An apparatus for transporting particulate material according to claim 1, wherein said primary transport channel is further defined by a second moving surface substantially opposed to said first moving surface, said second moving surface being moveable between said inlet and said outlet toward said outlet. 10. An apparatus for transporting particulate material according to claim 9, wherein said first moving surface comprises a first face of a first rotary disk and said second moving surface comprises a second face of a second rotary disk and said transport channel is further defined by at least one arcuate wall extending between said inlet and said outlet. 11. An apparatus for transporting particulate material according to claim 9, wherein each of said first and second moveable surfaces has at least one undulation defining a downstream facing drive surface for engaging particulate material. 12. An apparatus for transporting particulate material according to claim 1, wherein said first moveable surface has at least one undulation defining a downstream facing drive surface for engaging particulate material. 13. An apparatus for transporting particulate material according to claim 1, wherein said outlet duct has a bottom end portion adjacent said primary transport channel, an external end portion opposed to said bottom end portion, and an upwardly inclined internal wall to allow particulate material within said outlet to be compressed by gravity when said primary transport channel and said outlet duct are filled with particulate material, and further said internal wall having a cross-section which is outwardly diverging toward said external end portion. 14. An apparatus for transporting particulate material according to claim 13 further comprising a pressure vent provided adjacent a junction between said inlet duct and said transport channel. 15. An apparatus for transporting particulate material according to claim 13 further comprising a pressure vent through said internal wall of said outlet duct. 16. An apparatus for transporting particulate material according to claim 1, wherein said apparatus is operable to transport particulate material into a pressurized system containing pressurized fluid, and wherein the outlet duct has a first end coupled to the transport channel and a second end operable to be coupled to the pressurized system, said apparatus further comprising a non-return valve system for inhibiting pressurized fluid from entering into said transport channel through said outlet. 17. An apparatus for transporting particulate material according to claim 1, wherein said outlet duct has an internal wall, said internal wall which is coated with a low friction material. 18. An apparatus for transporting particulate material according to claim 17, wherein said low friction material is polytetrafluoroethylene. 19. An apparatus for transporting particulate material comprising: a housing having an inlet and an outlet, said outlet being upwardly angled to upwardly move particulate material therethrough; a transport duct enclosed within said housing between said inlet and said outlet having a primary transport channel, said primary transport channel being defined by first and second rotary disks movable relative to said housing between said inlet and said outlet towards said outlet and at least one arcuate wall extending between said inlet and said outlet, said first rotary disk having a first face, said second rotary disk having a second face which substantially opposes said first face, an outlet duct coupled to receive particulate material from said primary transport channel and defining a receptacle for holding, during the operation of the apparatus, a mass of the particulate material being transferred by the apparatus, so as to form a moving dynamic plug for inhibiting fluid from entering the primary transport channel from the outlet duct. 20. An apparatus for transporting particulate material according to claim 19, wherein said first and second faces each having at least one discontinuity configured to define first and second transport facilitation zones contiguous with said primary transport channel such that particulate material within said first and second transport facilitation zones are contiguous with particulate material within said primary transport channel, each of said discontinuities having at least one downstream facing drive surface. 21. An apparatus for transporting particulate material according to claim 19, further comprising drive means for moving said first and second rotary disks between said inlet and said outlet towards said outlet. 22. An apparatus for transporting particulate material according to claim 19, wherein said outlet duct has an outwardly diverging cross- section. 23. An apparatus for transporting particulate material according to claim 19, wherein said outlet duct has a bottom end portion adjacent said primary transport channel, an external end portion opposed to said bottom end portion, and an upwardly inclined internal wall. 24. An apparatus for transporting particulate material according to claim 19, wherein said apparatus is operable to transport particulate material into a pressurized system containing pressurized fluid, and wherein the outlet duct has a first end coupled to the primary transport channel and a second end operable to be coupled to the pressurized system, said apparatus further comprising a non-return valve system for inhibiting pressurized fluid from entering into said transport channel through said outlet. 25. A method of operating an apparatus for transporting particulate solids, said apparatus having an inlet, an outlet duct, a transport channel between said inlet and said outlet duct, said outlet duct being coupled to a pressurized system, and a moving surface contiguous with said transport channel for moving particulate solids through said transport channel toward said outlet, said method comprising the steps of: receiving particulate solids in said transport channel; sequentially forming moving cumulative bridges of particulate material within said transport channel; moving the bridged particulate material from the transport channel, upwardly through said outlet so as to fill said outlet duct with particulate material; and sealing said pressurized system by said moving cumulative bridges of particulate material. 26. A method according to claim 25, wherein said pressurized system contains a pressurized fluid, and said method further comprises the step of venting said gas adjacent a junction between said transport channel and said outlet duct. 27. A method according to claim 28, wherein said pressurized system contains a pressurized fluid, and said method further comprises the step of venting said gas in said transport channel. 28. A method of making an apparatus for imparting a drive force for driving a particulate material, the method comprising: determining a total pump operating pressure P; determining a drive force value F so that F > P; calculating at least one value for each of D and W from the relationship: F = f(D/W); forming a hub and a pair of rotatable disk members to be connected to said hub, said hub having a diameter D; arranging the pair of rotatable disk members coaxially and spaced from each other by a distance W; forming a peripheral wall adjacent the space between the pair of rotatable disk members so as to define a duct of with W in the space between the disk members and adjacent the peripheral wall; and forming a duct inlet and a duct outlet in material flow communication with the duct. 29. A pump made according to the method of claim 28. 30. A method according to claim 28, wherein each drive wall defines a drive surface facing the space between the drive walls, said method further comprising the step of forming at least one downstream facing surface on the drive surface of at least one of the drive walls. 31. A pump for imparting a drive force F to drive a material against a total pump operating pressure P, the pump comprising: a pair of spaced apart rotatable disk members; a hub connected to the rotatable disk members, said hub having a diameter D, said disk members being arranged coaxially and spaced from each other by a distance W, such that F = f(D/W), and F > P; a peripheral wall adjacent the space between the pair of disks and defining a duct of width W in the space between the disks; a duct inlet in flow communication with the duct; and a duct outlet in flow communication with the duct. 32. A method of making an apparatus for imparting a drive force for driving a particulate material, the method comprising: determining a total pump operating pressure P; determining a drive force value F so that F > P; calculating at least one value for each of L and W from the relationship: F = f(L/W); arranging first and second moveable drive wall members adjacent and spaced from each other by a distance W; forming a third wall adjacent the space between the first, and second drive wall members so as to define a duct of width W and length L in the space between the drive wall members and adjacent the third wall; and forming a duct inlet and a duct outlet in material flow communication with the duct. 33. A pump made according to the method of claim 32. 34. A method according to claim 32, wherein each drive wall defines a drive surface facing the space between the drive walls, said method further comprising the step of forming at least one downstream facing surface on the drive surface of at least one of the drive walls. 35. A method of making an apparatus for imparting a drive force for driving a particulate material, the method comprising: determining a total pump operating pressure P; determining a drive force value F so that F > P; calculating at least one value for each of L and S from the relationship: F = f(L/S); arranging first and second moveable drive wall members adjacent and spaced from each other by a distance W; forming a third wall adjacent the space between the first and second drive wall members so as to define a duct of cross-sectional area S and length L in the space between the drive wall members and adjacent the third wall; and forming a duct inlet and a duct outlet in material flow communication with the duct. 36. A pump made according to the method of claim 35. 37. A method according to claim 35, wherein each drive wall defines a drive surface facing the space between the drive walls, said method further comprising the step of forming at least one downstream facing surface on the drive surface of at least one of the drive walls. 38. A method of making an apparatus for imparting a drive force for driving a particulate material, the method comprising: determining a total pump operating pressure P; determining a drive force value F so that F > P; calculating at least one value for H from the relationship: F = f(H) ; arranging first and second moveable drive wall members adjacent and spaced from each other; forming a third wall adjacent the space between the first and second drive wall members so as to define a duct in the space between at least a portion of each drive wall member and adjacent the third wall, wherein the portion of each drive wall member defining the duct has a height H; and forming a duct inlet and a duct outlet in material flow communication with the duct. 39. A pump made according to the method of claim 38. 40. A method according to claim 38, wherein each drive wall defines a drive surface facing the space between the drive walls, said method further comprising the step of forming at least one downstream facing surface on the drive surface of at least one of the drive walls. 41. A method according to claim 38 further comprising the step of compacting particulate solids within said transport channel to form cumulative bridging of particulate solids in said transport channel. 42. An improved apparatus for transporting particulate material of the type having a movable wall structure defining a transport channel and having an inlet for receiving particulate material into the channel and an outlet for emitting particulate material from the channel, wherein the movable wall structure defines at least one wall moveable in the direction from the inlet toward the outlet for imparting a force directed toward the outlet on particulate material entering the channel from the inlet, the improvement comprising: a shroud plate assembly having a first plate covering a portion of the moveable wall adjacent the inlet for inhibiting the moveable wall from imparting a force on the particulate material as the material passes through the inlet. 43. An apparatus for transporting particulate material according to claim 42, wherein said moveable wall structure further comprises a second wall moveable in the direction from the inlet toward the outlet and wherein said shroud plate assembly comprises a second plate covering a portion of the second moveable wall adjacent the inlet for inhibiting the second moveable wall from imparting a force on the particulate material as the material passes through the inlet. 44. An apparatus for transporting particulate material according to claim 42, wherein at least a portion of the shroud plate assembly extends into the channel. 45. An apparatus for transporting particulate material according to claim 43, wherein at least a portion of the shroud plate assembly extends into the channel, between the two moveable walls. 46. An apparatus for transporting particulate material according to claim 43, wherein each respective moveable wall comprises a face of a respective rotary disk, said apparatus further comprising a hub coupled to each rotary disk, wherein said primary transport channel has an initial feed area adjacent a junction between said inlet and said primary transport channel and being generally defined between said inlet and said hub, and wherein said shroud plate assembly substantially covers said face of said rotary disk to substantially inhibit the disks from imparting a tangential force on particulate material entering in said initial feed area from the inlet. 47. An improved apparatus for transporting particulate material of the type having a movable wall structure defining a transport channel and having an inlet for receiving particulate material and passing the particulate material into the channel and an outlet for emitting particulate material from the channel, wherein the movable wall structure defines at least one wall moveable in the direction from the inlet toward the outlet for imparting a force directed toward the outlet on particulate material entering the channel from the inlet, the improvement comprising: a propelling device disposed adjacent the inlet for imparting a force directed toward the channel on particulate material passing through the inlet within the vicinity of the propelling device. 48. An apparatus for transporting particulate material according to claim 47, wherein said moveable * wall structure further comprises a second wall spaced apart from the first wall and moveable in the direction from the inlet toward the outlet and wherein said propelling device is disposed to impart a force directed toward the space between the two moveable walls on particulate material passing through the inlet within the vicinity of the propelling device. 49. An apparatus for transporting particulate material according to claim 47, wherein the propelling device comprises a paddle wheel device. 50. An apparatus for transporting particulate material according to claim 47, wherein the propelling device comprises a drive roller device. 51. An apparatus for transporting particulate material according to claim 47, wherein the propelling device comprises a fluid blower device. 52. An apparatus for transporting particulate material according to claim 47, wherein the apparatus further comprises a first wall located on the downstream side of the inlet, relative to the direction of movement of the moveable walls, the first wall being positioned such that at least a portion of particulate material passing into the inlet is directed by moveable walls toward the first wall, and wherein the propelling device is provided adjacent the first wall. 53. An improved apparatus for transporting particulate material of the type having a movable wall structure defining a transport channel and having an inlet for receiving particulate material into the channel and an outlet for emitting particulate material from the channel, wherein the movable wall structure defines at least one wall moveable in the direction from the inlet toward the outlet for imparting a force directed toward the outlet on particulate material entering the channel from the inlet, the improvement comprising: a first wall located on the downstream side of the inlet, relative to the direction of movement of the moveable walls, the first wall being positioned such that at least a portion of particulate material passing into the inlet is directed by the moveable wall toward the first wall, and a second wall located on the upstream side of the inlet relative to the direction, of movement of the moveable walls and extending into the transport channel, the second wall being positioned such that at least a portion of particulate material passing into the inlet is directed by the moveable wall away from the second wall; wherein the second wall defines a concavity in the inlet, adjacent the transport channel. 54. An apparatus for transporting particulate material according to claim 53, wherein the first wall defines a concavity in the inlet, adjacent the transport channel. 55. An apparatus for transporting particulate material according to claim 53, further comprising a shroud plate assembly having a first plate covering a portion of the moveable wall adjacent the inlet for inhibiting the moveable wall from imparting a force on the particulate material as the material passes through the inlet. 56. An apparatus for transporting particulate material according to claim 55, wherein said moveable wall structure further comprises a second wall moveable in the direction from the inlet toward the outlet and wherein said shroud plate assembly comprises a second plate covering a portion of the second moveable wall adjacent the inlet for inhibiting the second moveable wall from imparting a force on the particulate material as the material passes through the inlet. 57. An improved apparatus for transporting particulate material of the type having a pair of spaced apart movable walls defining a transport channel therebetween and having an inlet for receiving particulate material into the channel and an outlet for emitting particulate material from the channel, wherein the movable wall structure defines at least one wall moveable in the direction from the inlet toward the outlet for imparting a force directed toward the outlet on particulate material entering the channel from the inlet, the improvement comprising: a first wall located on the downstream side of the inlet, relative to the direction of movement of the moveable walls, the first wall being positioned such that at least a portion of particulate material passing into the inlet is directed by the moveable wall toward the first wall, and a second wall located on the upstream side of the inlet relative to the direction of movement of the moveable walls and extending into the transport channel, the second wall being positioned such that at least a portion of particulate material passing into the inlet is directed by the moveable wall away from the second wall; wherein the inlet defines an inlet opening, between the first and second walls and between pair of moveable walls, through which particulate material may pass into the channel, the inlet opening defining a cross-section shape having a first width at the first wall side of the inlet opeing and a second width at the second wall side of the inlet opening, said first width being greater than said second width. 58. An apparatus for transporting particulate material according to claim 57, wherein said first width is approximately three times larger than said second width. 59. An apparatus for transporting particulate material, comprising: a transport duct defining a channel having an inlet for receiving particulate material and an outlet for emitting particulate material; a first wall moveable adjacent the channel in the direction from the inlet toward the outlet, for imparting a force directed toward the outlet on particulate material entering the channel from the inlet; a shroud plate assembly having a first plate covering a portion of the first moveable wall adjacent the inlet for inhibiting the first moveable wall from imparting a force on the particulate material as the material passes through the inlet. 60. An apparatus for transporting particulate material according to claim 59, further comprising a second wall facing the first moveable wall and arranged adjacent the channel, said second wall being moveable in the direction from the inlet toward the outlet and wherein said shroud plate assembly comprises a second plate covering a portion of the second moveable wall adjacent the inlet for inhibiting the second moveable wall from imparting a force on the particulate material as the material passes through the inlet. 61. An apparatus for transporting particulate material according to claim 60, wherein at least a portion of the shroud plate assembly extends into the channel, between the two moveable walls. 62. An apparatus for transporting particulate material according to claim 59, further comprising: a first inlet wall located on the downstream side of the inlet, relative to the direction of movement of the moveable walls, the first inlet wall being positioned such that at least a portion of particulate material passing into the inlet is directed by the first moveable wall toward the first inlet wall, and a second inlet wall located on the upstream side of the inlet relative to the direction of movement of the moveable walls and extending into the channel, the second inlet wall being positioned such that at least a portion of particulate material passing into the inlet is directed by the first moveable wall away from the second inlet wall; wherein the second inlet wall defines a concavity in the inlet, adjacent the channel. 63. An apparatus for transporting particulate material according to claim 62, wherein the first inlet wall defines a concavity in the inlet, adjacent the channel. 64. A method for making apparatus for transporting particulate material, comprising the steps of: providing a first movable wall defining a transport channel; providing an inlet in particle flow communication with the transport channel; and disposing a first shroud plate within the inlet and extending over a portion of the first movable wall. 65. A method according to claim 64, further comprising the steps of: providing a second moveable wall adjacent and spaced apart from the first movable wall, wherein the space between the first and second movable walls defines the transport channel; and disposing a second shroud plate within the inlet and extending over a portion of the second movable wall. 66. A method according to claim 65, wherein the steps of providing first and second moveable walls comprises the steps of: arranging first and second disk members adjacent and spaced apart from each other; and supporting the first and second disk members for rotational motion. 67. A method for transporting particulate material in a channel between two movable walls, comprising the steps of: passing particulate material in an inlet provided in particle flow communication with the channel; covering at least a portion of each moveable wall with a shroud plate disposed adjacent the inlet; and passing particulate material from the inlet, adjacent the shroud plate, into the channel.

Inventors: HAY ANDREW G, HAY, ANDREW, G.
Applicants: STAMET INC, STAMET, INC.
Application year: 1994
Main classification: B65G31
IPC codes: B65G31, B65G65, F04D5, F04D7, F04D15, F04D29